I have created a new .fmp12 database file, which I instantly put on Server after changing the still persistent stuff like File Options - Spelling etc.
Then I imported data tables from anoter (local) file using the option to create a new table. It seems the theme is Cool Gray. I wonder if it depends on the initially selected theme for the file? Any observations?
When you are in layout mode you are on some specific layout. Using the New Layout option from that point will replicate any theme choice selected for the layout from which you started the New Layout process.
This can be a good thing if you are aware of it and intentionally choose the layout from which to start the New Layout process.
Otherwise it's a surprise!